As is well known in the art of gaseous combustion, in a volume of mixed combustible gas and air, flame will progress through the gas air mixture according to a certain velocity of propagation of the flame front. When the gas issues from a burner nozzle, the velocity of the gas mixture must be greater than the velocity of the flame front, so that the flame will always remain at a minimum distance from the surface of the burner. If the flow rate of gas reduces to a value less than the velocity of the flame front, the flame will progress upstream of the gas and may enter the burner. Combustion will then occur within the burner structure with consequent damage and danger to the equipment.
To prevent this progress of the flame front upstream of the gas flow, a structure is provided which is well known as a flame arrester, which generally comprises a structure having a plurality of small channels through which the gas flows. The walls of the channels are metal and are nominally at a temperature which is well below the ignition temperature of the gas. As flame tends to move upstream of the gas issuing from the arrester and into the interstices of the arrester, it will be cooled to a temperature below the combustion point, and the gas flame will be extinguished. The condition known as "flashback" in burners is an example of undesirable flame front movement.
Air is the typical source of oxygen for fuels burning. Therefore, in mixtures of air with typical non-detonative fuels and in typical burner operation, the flow velocity of the air-fuel mixture is greater than the velocity of the flame propagation, and flashback cannot occur. Detonative fuels are, for example, hydrogen, acetylene, ethylene oxide, carbon disulphide. With these fuels, flame arrest is impossible, unless a water seal is used, because of greatly excessive velocity of the flame front. Typical flame arresters, which are labyrinthine in structure, are therefore of no use with detonative fuels. Non-detonative fuels are typically hydrocarbon derivatives, C0 and the like, or more specifically the standard fuels of commerce and industry.
There are many cases where flame arrest is demanded for safety or for operations. Perhaps the first instance of useful flame arrest is to be found in what is called a "miner's lamp", as invented by Sir Humphrey Davy. In this device a metallic screen surrounds the flame of the lamp. When the lamp is within an atmosphere which is so laden with combustible gases as to be explosive upon contact with the flame, the metallic screen, which is interposed between the flame of the lamp and the explosive atmosphere, very rapidly chills the flame due to burning of combustible gas inside the screen so that flame created ignition temperature of the combustible gas cannot exist outside the screen, and no combustible burning or explosion can occur. Those versed in the arts know that the action of the flame arrester is due to simple flame front chilling to a temperature less than the ignition temperature of the fuel, and burning is thus checked. There is little danger of flashback in normal air-fuel flow operations. However, danger of flashback increases rapidly as flow velocity of the gas-air mixture is decreased, and is greatest when all fuel-air flow stops.
In the prior art the conventional type of flame arrester is cylindrical in shape, and involves a construction utilizing a plurality of cylindrical sheets with a corrugated thin sheet of metal inserted between each of the sheets, so as to form a large multiplicity of channels of triangular cross-section. Because of the large volume of metal involved in that type of structure, the cross-section for air passage is normally no more than 30% of the area of the flame arrester. Furthermore, because of the cylindrical construction, the shape is such as to provide poor space conservation. Consequently, the current present day flame arresters are large and bulky and have high pressure drop.